Radio receiving circuits



June 5 1923. Y 1,457,447

J. M!LLS RADIO RECEIVING CIRCUITS Filed Dec. 22 1921 /m/e/7f0/-.- John I/VI/AS, v

Patented June 5, 1923.

UNITED STATES P'A 1,457,447 TENT OFFICE.

JOHN MILLS, OEWYOMING, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

RADIO RECEIVING CIRCUITS.

Application filed December 22, 1921. Serial No. 524,070.

T all whom it may concern: Be it known that 1, JOHN MILLs, a cit zen of the lfnited States, residing at \Vyommg, in the county of Essex, State of New Jersey, i have invented certain new and useful Tmproveinents in Radio Recelving Circuits,

of which the following is a full, clear, concise, and exact description. This invention relates to radio receiving 1 circuits and particularly to that type employing the principle of successive detection.

The term successive detection ashere used is given its usual signification as 1nvolving the function of stepping down the frequency of the received radio frequency waves to an intermediate high frequency by one detecting operation and employing a subsequent detecting operation to obtain the low frequency modulating component.

cording to the present invention the Wave to be received and an auxiliary radio wave are received and impressed together upon the input circuit of the first detector by which the first frequency reduction is accomplished. The auxiliary wave is given such a frequency that, by combination with the normally received wave, there will result in the output circuit of said detector an intermediate frequency wave having. a desired periodicity. The auxiliary wave source may have its sole functionas above indicated or it may combine this function with that of a source for transmitting waves to the distant station, the circuits associated with said source and the receiving circuits constituting the terminal circuits of a complete two-way channel. A system characterized generally by the production of in- 40 termediate frequency waves at the receiver will be designated an intermediate frequency system, the specific type in which the auxiliary Wave source has a double function, as described, being correspondingly designated a modified intermediate frequency system. A receiving circuit having means for stepping down the frequency of its normally received wave by combination with an auxiliary frequency wave, whether said auxiliary wave has the additional function mentioned or not, will be designated'an,

intermediate frequency receiving circuit.

The auxiliary frequency source will be designated as a local source and its circuit as the local transmitting circuit.

It is characteristic of intermediate frequency systems that most efiicient operation requires a critical amount of transmission from the auxiliary wave source, this amount being limited, in part, by the inability of the high frequency detector to handle more thana critical value of this current without impairment of its function. In a modified intermediate frequency system of the form in which the transmitting and receiving circuits terminate in a common low frequency circuit, there is the additional limitation imposed by the tendency of the circuits at a station to sing if. acritical value of auxiliary current is exceeded.

The principal object of the present invention is to provide a means whereby, in an intermediate frequency receiving circuit a regulable amount of auxiliary radio carrier wave may be impressed 0n the input circuit of the first detector without detriment to reception from the distant station.

A specific object is to provide means whereb the function described in the statement 0 the principal object may be accomplished without regard to the relative directions of the distant and local transmitting circuits with respect to the receiving circuit. i

An additional object is to provide means for the accomplishment ofthis function involving the use of a single directive antenna selective to only one of the two frequencies involved, namely, that of the signal modulated wave to be received. A still further object is to provide in a system of this kind means whereby an initial adjustment of the amount of auxiliary carrier wave is caused to persist even though said antenna is adjusted so as to be, by reason of its directive characteristics, more or'-less favorably related to the local transmitting station than at the time of said initial adjustment.

The means of the invention comprises, in one modification, a receiving antenna comprising a series arrangement of directive loops independently rotatable and respectively tuned to the frequencies of the distant and local transmitting circuits The two frequencies are sufiiciently spaced so as to provide the desired intermediate frequency and so that each loop has relatively low imby waves of two different frequencies, each of which is adjustable in amplitude, may be superposed on the input circuit of a detectran mitted'from the distant transmitting station is used. The loop islconnected tothe first detector through a vacuum, tube am plifier, or other unilaterally conducting device across the output circuit of which is v placed a variable shunt consisting efa series arrangement of inductive and capacitive elements adjusted to. resonance at the frequencyjof the local transmitting circuit, In series with these elements is'an adjusta ble resistance which constitutes, withthe remaining portions of the circuit, an adjustable impedance means. The resistance adjust- ,ing means for this. circuit is mechanically' coupled 4 with :the rotating means of .the directive loop in such ner that when said .loopis oriented so I as to receive with'maximuniintensity from cuit The mechanical couplin' and Fig. 2 illustrates substituted for those. shown" at the left to give the alterna-' the local transmittin'gcircuit, the shunting effect of the circuit is a maximum, and sufiicient to give the proper amount of the auxiliary wave in the outputcircuit of the first detector. As the loop is. oriented from this position in. order to receive with maximum intensity from a distant station, the loop becomes relatively less favorably positioned with regard. to the related transmitting cirmeans by introducing resistance in the s nnt circuit correspondingly reduces the shunting effect and accordingly tends to automatically maintain the'amou'nt of the auxiliary current constant.

description lustrates a system using two receiving loops, circuits wh ch may be of line X-X of Fig. 1

tive form of the invention using a single receiving loop. I I

In the figures ofthe drawing, the circuits most closely related to the means of the invention are shown in detail and the' remaining circuits in diagrammatic form only.

Throughout the drawing-the component elements are identified, so far as possible, reference letters so chosen as to be sug gestive of the function of said elements, subscripts being used to distinguish between different elements of a kind.

Referring to Fig. 1, there is shown a station including the transmitting and receiving antennae AN, and AN respectively,

said station being designed to communicate with a'distant station provided with transmitting antenna AN The remaining 'circuits at the distant station man- . antenna A imum intensity.

. from antenna AN are notshown, it being understood that they may be of the character more fully disclosed in connection with antennae AN and AN or of any other type capable of transmitting and receiying modulated radio frequency waves. The circuits'of the station at the right provide means whereby low frequency signals originating in line -1 may be transmitted as modulations of a radio frequency carrier Wave from transmitting antenna AN 1 to the distant station, and whereby signal modulated carrier waves similarlytransmitted from the antenna" AN ,may be received by. antenna AN detected, and the modulating component'thereof transmitted to the circuit-l. In orderto unite the. functions of the'outgoing and'incoming low frequency circuits in a single circuit 1, as'described, a balanced three-winding transformer 'or by- 'brid coil arrangement with a balancing network N is used, accordin to a principle well understood in the art. bviously, the principle of the invention is broad enough to include other arrangements than that shown, and may be applied, for example, to an ar rangement in which the low. frequency transmitting and receiving circuits are distinct. v

The transmitting circuit is conventionally represented by the low frequency circuit 2, theoscillator O, the modulator M, the ampliand the transmitting antenna 'AN This typifies any suitable system for 'im-, pressing high frequency modulated wave on 1\ The receiving circuit is represented by the-receiving antenna AN the high fre- 'quency detector CD the intermediate fre- F or a further disclosure of the invention;

quency detector D and the low; frequency circuit 3. The antenna AN comprises two directive'loops 4 and 5 in series, each including a capacity element as shown, for" the purpose of providing adjustment of the frequency at which it is resonant. The loops 11o are'independently rotatable and .are respectively resonant to the'waves from antennae AN, and AN,. The loop 4 is normally oriented so as to receive waves from the distant communicating station with amax- By reason of its resonance to a different frequency, it is able to discriminate against the frequency ofwaves from the local transmitting antenna 'AN y However, loop 5 is resonant to the latter 1 frequency and accordingly permits a potential to be built up between its terminals which has a valuedepending 0n the angle of presentation of said loopto the direction of incidence of-waves from antenna AN,. 1 5v Since loop 4 has low impedance to the'wavcs and correspondingly loop 5 has a low impedance with respect to-waves from antenna AN there is pro-. vided a means whereby a regulable amount of each of the two waves may be, substantially independently of the other, impressed on the input of detector D,. In operation,

after adjustment of loop 4, so as to give a maximum intensity of signals, loop is oriented until the desired amplification of .the signal, as measured in the love fredifference of the normally received and auxiliary wave frequencies which is selected by circuits 6 and 7 which are resonant to said frequency and impressed on intermediate!v frequency detector 1),. Tht output'currnt of detector D contains a separable com-' ponent of the signal frequency, which is utilized in the low frequency circuit 1.

The loops4 and 5 are preferably of different size on account of the difference in distances of the transmitting stations from which they are designed to receive, loop 4 accordingly being the larger. For a similar reason the two loops may have a different number of turns. Although tuned circuits are shownbetween detectors D and D other forms of selective circuits such as, for

example, filter circuits, may be substituted therefor, as is well known. A selective circuit of'any type may be inserted between the detector D and the hybrid connection in order to eliminate from the low frequency circuit undesired currents resulting from detection. Although the minimum number of vacuum tube devices for the accomplishment of the 'necessary functions has been shown, in many cases the detecting .devices may give insufficient amplification,

in which case additional tubes arranged to give distortionless amplification may be in serted in' the circuit as desired, as 1n the input circuits of the detecting tubes or in the output c rcuit of detector D The system of Fig. 2 differs from that of Fig. 1 in the use of a single directive loop and in the addition of an unidirectional conducting device A between the antenna and the high frequency detector. This device is here shown as an amplifier or repeater although its function as such is incidental to its primary function of separating the shunt circuit 8, shown connected across its output, from the receiving antenna. so that the function of the antenna is unaffected by the presenceof the shunt circuit or by adjustment thereof.

The antenna is tuned to the frequency of the distant station and is rotatably mounted. During normal operation it is oriented to such position as to receive the waves the directive and selective functions of the antenna are here combined in a single loop as distinguished from the system of Fig. 1.

In order that the intensity of the wave received from the local transmitting circuit may be independently adjustable and may maintain such adjustment as the loop is oriented .to receive from variously located distant stations, the shunt circuit 8 is provided. This circuit is tuned to the frequency of the local transmitting circuit and contains an impedance "arying element 9, the circuit thus constituting a variable shunt for the auxiliary wave. The impedance varying means is shown as a. resistance for reasons which will be hereinafter explained.

.The impedance is initially adjusted so that, with the loop most favorably positioned with respect to the local transmitting circuit, the proper amount of auxiliary wave energy from said circuit is incident on detector D The orienting loop and impedance varying means are mechanically coupled in such manner that as the loop is rotated from its initial position in either a clockwise or counter-clockwise direction, the shunting effect will be decreased at such a rate as to maintain the intensity of the auxiliary wave incident on the detector D constant. In the particular arrangement shown the centrally-positioned contact 10 is connected to the end of resistance element 9, so that when contact arm 11 is on this contact the shunting effect is a maximum, the contact 11 being associated with the loop in such manner that this position of contact 11 corresponds to the initial position of the loop. For this position, the impedance is adjusted as by varying resistance R to give the proper shunting effect. Pairs of contacts 10 equally spaced from the central contact are connected together and to resistance 9 in such a manner that the shunting effect is decreased in the manner above described asthe loop is rotated in either direction from the initial The are formed by contacts 10 the magnitude of resonant to a frequency differing by a considerable amount from the frequency. of the waves from thedistant station, it will at all times constitute an-inefficient shunt'forci r rent of said frequency. The impedance varying function maybe secured by detuning, theshunt circuit;''in'stead of'by the method shown. The. methoddescribed is the one preferred since by itsuse'the variable shunting to the auxiliary wave f'requency. Further, the variation ofimpedance effected by the more closely the energy local source obey the lawof variation of incident on the detector from the as the loop. is oriented. Aecordin'gly such variation of energy can be more completely compensated. Filters and amplifiers may be used in the circuits of this figure in the man- ,ner described in the description of' Fig. 1.

' Although the principleof the invention has been embodied, for purposes of illustra- .tion, in a'system in which thelocal radio;

source has a dual function, it should be understood that the invention, in its bro'ad con.- ception, is independent of the particular type of circuit associated with said source.

I It should further be understood that al two independentlyrotat'able directive loops though an inaudible intermediate frequency ligs" been assumed, the theory and modeof operation apply equallywell to the case of an audible intermediate frequency. The low frequency impulses or signals may be speech or telegraph currents,

ticular signaling wave.

lYliat is claimed is: y

l. A receiving antenna I comprising a series arrangement of twov directive' loops, re-

spectively tuned to different frequencies,-

said loops being independently rotatable.

2., A receiving circu t comprising, in combination, a receivingconductor consisting of connected in series andrespectivelyresonant to different frequencies, and two detecting devices connected in tandenito said conduc: tor.

v I 3. A receiving circuitcomp rising, in com 'b nation, two independently rotatable loop ,antennae connected in seriesandrespectivelytuned to different frequencies, a detector electrically connected to-saidantennae, circuitmeans for selecting from saidcleteetor a modulated differencefrequency, component, and circuit means for impressing said component on asecond detector.

- 4. A radio system comprising a source of radio carrier waves, a second source of radio carrier waves having a different frequency,

a receiving conductor for said waves, and

means electrically coupled therewith for combining waves from said sources, said receiving conductor comprising two independently rotatable directive loops connected in effect ismore n'early. confined ence frequency component although the claims are not intended to be solimited to any parfrequency wave,

means for producing and radiating a carrier wave, and means for receivingand deriving signals from an incomingmodulated carrier wave having a frequency differing by an inaudible amount from that of said first mentioned wave, said last mentioned means com prising a series I arrangement of two independently rotatable directive loops,. re-

spectively tuned to the two carrier Wave frequencies, whereby a portion of the outgoing wave is received with the incoming wave, means for combining said ,received waves, means for selecting the modulated differof the resultant wave, and means for detecting said/ difference frequency wave. V i

6. A duplex radio station comprising, in combination, a low frequency transmitting circuit for signals, a source of carrier waves, means for modulating said waves in accord ance with said signals, means for radiating said modulated-carrier waves, and a receiv-- mg circuit for receiving and derivingsig nals from an incoming modulated carrier wave, said receiving circuit comprisin a directive loop tuned to the incoming waves, a

directive loop tuned to the. frequency, of

said source in series wit h said first mentioned loop, means for lating said loops, means for combining the received waves, means for' selecting the difference frequency component of said waves to produce an intermediate frequency wave, means for detecting frequency component from said interme iate and means conjugately relating the output circuit of said last 'mei'r independently rotioned detector and said low frequency cir-.

cuitf to a common circuit. 4 7. A receiving circuit comprising, in com bination, a directive receiving antenna tuned to the frequency of a desired wave, means for rotating said antenna, a unilaterally conducting device and a detecting device serially related to said antenna, av reactive shunting circuit positioned between said de-- vices, adjustable means for varying the-impedance of said shunting circuit, and coupling means between said rotating and adjustable means, whereby said coupled means may be'simultaneously actuated.

8: A receiving circuitcomprising a directive receiving antenna t med to a desired fre- 1 quency and having a rotating means, a thermionic repeating device and v a detecting device coupled in tandem to said antenna, a series resonant circuit tuned'to a'frequency differing from that of the antenna connected in shunt to the output of said device, a variable resistance means included in said resonant circuit, and mechanical coupling means between said antenna roand deriving the si nal repeating tating means and said resistance varying the output of said device and including a means whereby said coupled elements may variable resistance, and means adapted to be simultaneously actuated. simultaneously rotate said directive antenna 9. A duplex radio station comprisinga and vary said resistance, said last mensource for producing and radiating a carrier tioned means being adjusted so that said wave, a local directive receiving antenna circuit has a maximum shunting effect for tuned to a desired incoming wave having a said reinforcing wave when the antenna is difl'erent frequency for receiving said incompositioned to receive with maximum intening wave and a reinforcing wave from said sity from said radiating means. source, a thermionic repeating device and a In witness whereof, I hereunto subscribe detecting means connected in tandem to said my name this 20th day of December A. D. antenna, a series resonant circuit tuned to 1921.

the waves from said source connected across JOHN MILLS. 

